1. Field of the Invention
The present invention relates to a low temperature liquefied gas tank of the membrane type for housing low temperature liquefied gases such as petroleum gases which are in a gaseous state at atmospheric temperature and can be liquefied by being cooled under atmospheric pressure.
2. Description of the Prior Art
Conventionally, a tank for the aforementioned purpose is generally composed to an outer vessel of a rigid and pressure resistant structure, a compression resistant heat insulating layer provided at the inside of said outer vessel and an inner membraneous vessel provided at the inside of said heat insulating layer, said inner membraneous vessel being made of a relatively thin plate and adapted to be readily flexed by internal pressure applied thereto so as to come into close contact with the inner surface of said heat insulating layer, whereby the internal pressure is finally supported by the outer vessel by way of said heat insulating layer. With regard to a tank of this kind, in the case where the inner membraneous vessel has a rectangular parallelepiped shape having substantially spherical corner portions (generally called "ball corner"), portions A (FIG. 2.) adjacent to the spherical corner portions are subject to a high bending stress and there is the danger that a breakage may occur at portion A due to overstressing beyond the fatigue limit.